Various paint compositions are known for use on automotive and architectural glass. Such paints are used, for example, to form opaque borders around the peripheral marginal surfaces of glazings used as windshields, sidelites, and backlites of motor vehicles. These borders are used to obstruct from view attachment means for the glazings and protect adhesives which might be used from exposure to light which could degrade them.
Generally these compositions are ceramic compositions formed from a mixture of metal oxides in an organic (oil based) vehicle like mineral oil. The opaque peripheral marginal paint bands fired onto automotive glazings are generally black provided by colorant oxides like chrome oxide, cobalt oxide and nickel oxide. In view of environmental and commercial considerations, more desirable water-based paints have been developed for use in place of such organic vehicle paints. One such paint is disclosed in U.S. Pat. No. 5,698,026 commonly assigned herewith which advantageously is curable at relatively low temperatures compared to the relatively high temperatures generally required for ceramic/organic vehicle paint curing. Subjecting the glass to high temperatures to cure the paint can impart undesirable optical distortions into the glass sheets. More particularly, the '026 paint is a soda-lime silicate based paint which uses metal oxide pigment to color the glass. One of the drawbacks of the paint is that the color of the water based silicate paint is not as dark as the oil based paint having the same amount of metal oxide pigment. If these two different paints are used in the same automotive vehicle on different glazings, the color should be formulated to appear the same. And merely adding more metal oxide colorant to the water based silicate paint in an attempt to darken the color suitably is not effective to do so. Hence, it is necessary to find another way to darken the color of the silicate paint when desired without negatively affecting the excellent properties of the paint.
It is an object of the present composition to provide a water-based paint composition which is capable of displaying a dark color. It is a further object of the present invention to provide a water-based paint composition which is more opaque to light so as to protect adhesives therefrom. Another object of the present invention is to provide a paint with improved thermal expansion match properties to the glass substrate on which it applied.
These and other objects are accomplished by the present invention paint which is curable at relatively low temperatures and which exhibits excellent durability.